Amorphous polyaryletherketone and blends thereof for use in additive manufacturing

ABSTRACT

A material for use with a 3D printer comprises a polyaryletherketone (PAEK) having an amorphous morphology. In some embodiments, the material also includes one or more further compounds having an amorphous morphology. In some further embodiments, the material includes, in addition to an amorphous PAEK, a compound having a semi-crystalline morphology.

CROSS-REFERENCE

The present application is a continuation of International ApplicationNo. PCT/US2016/055505, filed Oct. 5, 2016, which is a continuation ofU.S. patent application Ser. No. 14/874,963, filed Oct. 5, 2015, each ofwhich is entirely incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to compositions for use inadditive manufacturing, more commonly known as “3D printing.”

BACKGROUND OF THE INVENTION

The additive manufacturing process is widely known as thethree-dimensional (“3D”) printing of objects. There are a variety of3D-printing processes, VAT polymerization, material jetting, binderjetting, material extrusion, powder bed fusion, sheet lamination, anddirected energy deposition.

Extrusion-based 3D printing involves the deposition of thermoplasticmaterials. This process fabricates a three-dimensional object from amathematical model of the object using materials such as thermoplasticsand metals that are typically in the form of a filament. In the case ofa thermoplastic material, the object is built by feeding a thermoplasticfilament into a heated extrusion head. The thermoplastic is heated pastits glass transition temperature and then deposited by the extrusionhead as a series of beads in a continuous motion. After deposition, thebead quickly solidifies and fuses with the beads next to and below it.The nozzle of the extrusion head follows a tool-path controlled by acomputer-aided manufacturing (CAM) software package, and the object isbuilt from the bottom up, one layer at a time.

Prototyping is currently the most common application for extrusion-basedprinting, using materials such as acrylonitrile butadiene styrene (ABS),polylactic acid (PLA), methyl methacrylate acrylonitrile butadienestyrene copolymer (ABSi), and polycarbonate (PC), among others.

Toward the end of printing production-suitable parts, higher-endengineering semi-crystalline and amorphous polymers, as well as metalsand ceramics with greater mechanical, chemical, thermal, and electricalproperties are being used. Examples of semi-crystalline polymersinclude, among others, semi-crystalline polyaryletherketones (PAEK),polyetheretherketone (PEEK), and polyetherketoneketone (PEKK). Examplesof amorphous engineering polymers include polyphenylsulphone (PPSU) andpolyetherimide (PEI), among others.

Amorphous polymers are relatively easy to process via materialextrusion. Unfortunately, these polymers tend to have relatively poorchemical resistance, poor heat resistance, and inferior mechanicalproperties such that the parts formed therefrom using material extrusionare often not suitable for production (as opposed to prototyping)applications.

Semi-crystalline thermoplastic PEEK, mentioned above, has exceptionallyhigh tensile and flexural strength compared to other polymers and canperform under load at high temperatures. Its chemical resistance andtolerance to steam and hot water have enabled its use in high-strengthapplications in the medical and oil & gas industries.

Although parts formed from PEEK have been printed using materialextrusion, this polymer introduces challenges to the 3D-printing processdue to its semi-crystalline morphology. In particular, more advancedbuild platforms and enclosures are required to manage the high ambienttemperature during printing. Furthermore, this semi-crystalline polymerhas a longer cooling time compared to lower temperature amorphousmaterials, which increases the minimum layer time and requires the useof cooling to speed up solidification. PEEK parts printed via materialextrusion also experience more significant shrinkage and warpagecompared to parts printed from amorphous materials. This leads todecreased dimensional accuracy and larger tolerances for PEEK partsprinted in this fashion. The increased warpage can also result in partseparation from the build surface unless high build-chamber temperatures(c.a. 280 to 310° Celsius) are used. Additionally, PEEK has higher meltflows requiring higher pressures during extrusion and printing comparedto amorphous materials.

To overcome the problems associated with printing via material extrusionusing PEEK, the present inventors have blended PEEK with other amorphousthermoplastics, as disclosed in U.S. patent application Ser. No.14/297,185. These compositions have been optimized for a materialsextrusion printing process allowing large, complex production parts tobe formed. Although easier to process than neat semi-crystalline PEEK,these PEEK blends do not exhibit the superior mechanical, thermal, andchemical resistivity properties of neat PEEK.

A need therefore remains for materials for use in 3D printing, viamaterial extrusion as well as other 3D printing techniques, that arerelatively easy to process and will result in printed parts that exhibithigh chemical resistance, high heat resistance, and high strength suchthat the parts can be used as a production/working part in relativelydemanding applications, such as arises in the aerospace, healthcare, andoil & gas industries.

SUMMARY

The present invention provides a material for use in 3D printing thatavoids some of the drawbacks of the prior art.

In accordance with the present teachings, a resin comprising anamorphous form of a (normally semi-crystalline) polyaryletherketone(PAEK) is used for forming production parts via 3D-printing techniques.PAEK thermoplastics useful in conjunction with embodiments of theinvention include, without limitation, polyetheretherketone (PEEK),polyetherketone (PEK), polyetherketoneketone (PEKK),polyetheretherketoneketone (PEEKK), and polyetherketoneetherketoneketone(PEKEKK).

In the illustrative embodiment, the PAEK is amorphous PEEK. To theextent this Detailed Description references PEEK or any other specificPAEK, such as those mentioned above, it is to be understood that theseteachings apply generally to any PAEK compound unless otherwisespecified. In various embodiments, the resin comprises:

-   -   one amorphous PAEK compound (e.g., PEEK, etc.);    -   one type of amorphous PAEK (e.g., PEEK, etc.) but at least two        versions thereof, each having a different measure of        amorphousness (i.e., one relatively less amorphous, one        relatively more amorphous) from the other;    -   two or more different amorphous PAEKs (e.g., PEEK and PEKK,        etc.);    -   at least one PAEK compound in amorphous form and at least one        amorphous compound that is not a PAEK compound;    -   at least one amorphous PAEK and at least one semi-crystalline        PAEK, wherein the PAEK compound is the same (e.g., amorphous        PEEK and semi-crystalline PEEK, etc.);    -   at least one amorphous PAEK and at least one semi-crystalline        PAEK, wherein each PAEK compound is different (e.g., amorphous        PEEK and semi-crystalline PEKK, etc.);    -   at least one amorphous PAEK and at least one semi-crystalline        compound that is not a PAEK compound;    -   combinations of the foregoing.

Semi-crystalline PAEK has a relatively high viscosity and melt flow andtherefore requires relatively high pressure to force it through anextrusion head of a 3D printer during printing. On the other hand,amorphous PAEK and blends thereof in accordance with the presentteachings exhibit the relatively more desirable rheological propertiesof a higher melt mass-flow rate that is characteristic of a lowertemperature, common amorphous polymer. In other words, the use ofamorphous PEEK orotheramorphous forms of other PAEK compounds decreasesthe viscosity sufficiently to reduce the pressure required to print thepolymer blend via a material extrusion technique.

Furthermore, semi-crystalline PAEK has an increased shrinkage andwarpage compared to amorphous polymers, requiring the use ofhigh-temperature heating beds, a slower print speed, and/or the use ofcooling to maintain geometrical accuracy around critical object featuresand to prevent the part from pulling off the build plate. The use ofamorphous PAEK or blends thereof in accordance with the presentteachings exhibit less warpage or shrinkage given its lower coefficientof thermal expansion and contraction. In other words, the use ofamorphous PAEK allows the material to adhere better to the build surfaceand may produce tighter geometrical tolerances.

The addition of amorphous PAEK to semi-crystalline PAEK can increase theheat resistance and maximum operating temperature compared toconventional materials used for 3D printing.

As previously noted, after it is prepared, the resin can be used toprint parts via material-extrusion 3D-printing techniques. However, insome other embodiments, parts are printed from the resin using other3D-printing techniques, such as, for example, directed energydeposition, sheet lamination, powder bed fusion, binder jetting, andmaterial jetting. With respect to its use with powder bed fusion, binderjetting, and material jetting techniques, the resin must be ground to anappropriate particle size. In embodiments in which the resin comprisesmore than a single compound, melt blending is used to blend thecompounds. Melt blending for extrusion is specific to material extrusionand directed energy deposition 3D-printing techniques. However, forpowder bed fusion, binder jetting, and material jetting techniques, meltblending is used to form the blend prior to grinding to form a powder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a flow diagram of a first method for preparing a blend ofpolymers, including at least one amorphous PAEK compound, in accordancewith an illustrative embodiment of the present invention.

FIG. 2 depicts a flow diagram of a second method for preparing a blendof polymers, including at least one amorphous PAEK compound, inaccordance with an illustrative embodiment of the present invention.

DETAILED DESCRIPTION

Although the illustrative embodiment is directed to the use of amorphousPEEK and blends thereof, any polyaryletherketone (PAEK) that can besynthesized to exhibit an amorphous morphology as disclosed herein, canbe used either alone or in a blend to print production-quality parts.

The crystallization of polymers is a process associated with partialalignment of their molecular chains. The fraction of the orderedmolecules in a polymer is characterized by the degree of crystallinity,which typically ranges between 10% and 80%, inclusive. For this reason,crystallized polymers are often called “semi-crystalline. A polymer withless than 10% crystallinity is considered to be “amorphous.” The degreeof amorphousness is the inverse of degree of crystallinity. For example,a polymer with a crystallinity of 5% has a greater degree ofamorphousness than a polymer having a crystallinity of 9%.

The degree of crystallinity is estimated by the different analyticalmethods' such as density measurement, differentia-scanning calorimetry(DSC), infrared spectroscopy, nuclear magnetic resonance (NMR), andX,-ray diffraction (XRD). In addition, the distribution of crystallineand amorphous regions (and hence degree of crystallinity) can bevisualized with microscopic techniques, such as polarized lightmicroscopy and transmission electron microscopy. The numbers for (degreeof) crystallinity provided herein are based on DSC, unless otherwiseindicated.

PAEK compounds are characterized by phenylene rings that are linked viaoxygen bridges (ether and carbonyl groups (ketone)). The ether-to-ketoneratio and the sequence thereof in the PAEK compound affects thecompound's glass transition temperature and melting point. This ratioand sequence also affects the heat resistance and processing temperatureof the PAEK. The higher the ratio of ketones, the more rigid the polymerchain, which results in a higher glass transition temperature andmelting point. The processing temperatures can range from about 350 to430° C.

PEEK is commercially manufactured as a semi-crystalline thermoplasticusing step-growth polymerization of bisphenolate salts. PEEK is usuallymanufactured with a degree of crystallinity in the range of about 25 to35%

In accordance with the illustrative embodiment and unlike conventionalpractice, PEEK is manufactured to exhibit an amorphous morphology (i.e.,lower degree of crystallinity) by altering the process conditions duringpolymerization.

One method to achieve amorphous PEEK is to continue the step-growthpolymerization, creating very high molecular weight grades. Thepolymerization processing conditions must be carefully controlled toenable the polymerization process to continue. For example, the amountof initial monomers added must be limited and precisely measured. Anexcess of one type of monomeric reagent over another can limit themolecular weight. The reactants must have a high purity to prevent theoccurrence of side reactions from contaminates. The viscosity of thepolymerization medium must be controlled to promote continued stepreactions. Finally, solid-state polycondensation can be used as apost-processing step to further increase the molecular weight.

Furthermore, incorporating certain additives during polymerization canprevent or restrict the organization of crystalline chains. For example,reactants containing bulky side groups (e.g., multiple benzene rings,etc.) can be added to the ends of the polymer chains. These bulky sidegroups prevent the polymer from organizing into a crystallinemorphology. Amorphous PEEK exhibits a higher toughness and ductilitycompared to semi-crystalline PEEK, but generally has a lower tensilestrength and chemical resistivity.

In light of the present disclosure, those skilled in the art will beable to apply the foregoing techniques and others to suitably controlthe polymerization process to produce amorphous PEEK and other amorphousPAEK compounds.

The amorphous PAEK compound can be extruded into filament for use in amaterial extrusion 3D-printing process. In some embodiments, asemi-crystalline PAEK compound and an amorphous PAEK compound areblended together to improve the mechanical performance (i.e., tensilestrength and Young's modulus) and increase the chemical resistance (asmeasured, for example, via ASTM D543) of the resulting printed part, ascompared to using an amorphous PAEK compound alone.

Semi-crystalline thermoplastics other than semi-crystalline PAEKcompounds can be blended with the amorphous PEEK to achieve specificmaterial properties or processing properties. For example and withoutlimitation, semi-crystalline resins such as polyimide, polyethylene,nylon, polyphenylene sulfide, and polyphthalamide can be used.

Also, amorphous compounds other than amorphous PAEK compounds can beblended with one or more amorphous PAEK compounds to achieve specificmaterial properties or processing properties. For example and withoutlimitation, amorphous resins such as polyetherimide (PEI commonly knownas Ultem®), polyethersulfone (PES), Polysulfone (PSU commonly known asUdel®), polyphenyl sulfone (PPSU commonly known as Radel®),polyphenylene oxides (PPOs), acrylonitrile butadiene styrene (ABS),polylactic acid (PLA), polyglycolic acid (PGA), polyamide-imide (PAlcommonly known as Torlon®), polystyrene (PS), polyamide (PA),polybutylene terephthalate (PBT), poly(p-phenylene sulfide) (PPS),polyethersulfone (PESU), polyethylene ether (commonly known asPrimoSpire®), and polycarbonate (PC) can suitably be used.

Thus, in various embodiments, a resin for a 3D-printing processincludes:

-   -   (i) One type of amorphous PAEK (e.g., PEEK, etc.);    -   (ii) One type of amorphous PAEK (e.g., PEEK, etc.) but at least        two versions thereof with differing degrees of amorphousness        (i.e., one relatively less amorphous, one relatively more        amorphous);    -   (iii) Two or more different amorphous PAEKs (e.g., PEEK and        PEKK, etc.);    -   (iv) At least one amorphous PAEK and at least one amorphous        compound that is not a PAEK compound;    -   (v) At least one amorphous PAEK and at least one        semi-crystalline PAEK, wherein the PAEK compound(s) is the same        (e.g., amorphous PEEK and semi-crystalline PEEK, etc.);    -   (vi) At least one amorphous PAEK and at least one        semi-crystalline PAEK, wherein the PAEK compound is the        different (e.g., amorphous PEEK and semi-crystalline PEKK,        etc.);    -   (vii) At least one amorphous PAEK and at least one        semi-crystalline compound that is not a PAEK compound; and    -   (viii) Any combinations of (i) through (vii). For example and        without limitation, variations on (v) or (vi) with (ii), wherein        multiple versions of the amorphous PEAK(s) with differing        degrees of amorphousness and/or multiple versions of the        semi-crystalline PAEK(s) with different semi-crystallinity; etc.

In some embodiments, the mixing or compounding of the blend of amorphousand semi-crystalline thermoplastic polymers (e.g., PEEK, etc.) takesplace before filament extrusion (for material extrusion and directedenergy deposition techniques). In such embodiments, the polymers areheated above their processing temperatures and are well mixed. Theresulting resin is a homogenous blend of multiple polymers.

In some other embodiments, the mixing or compounding of the blend ofamorphous and semi-crystalline thermoplastic polymers (e.g., PEEK, etc.)occurs through melt blending during filament extrusion (for materialextrusion and directed energy deposition techniques). In suchembodiments, the pellets of the polymers are mixed and then added to thehopper of the filament extruder. The materials are then melted in thebarrel and mixed as the extruder screw rotates. Although this method ismore cost-effective and requires one less step than pre-compounding, itmay not yield a completely homogenous polymer blend.

In some embodiments, the weight ratio of (total) amorphous PAEK to(total) semi-crystalline PAEK is in a range of about 50:50 to about95:5, inclusive. The ratio selected for any particular application mayvary primarily as a function of the materials used and the propertiesdesired for the printed object.

The blend of amorphous PEEK with semi-crystalline PEEK can result inmiscible, immiscible, or compatible polymer blends. If the polymers aremiscible, the blend will have one glass transition temperature modeledby the Fox Equation:

$\frac{1}{T_{g}} = {\frac{w_{1}}{T_{g \cdot 1}} + \frac{w_{2}}{T_{g \cdot 2}}}$

-   -   where: T_(g) is the glass transition temperature

Considering a specific example, if PEEK (T_(g)=143° C.) is blended withpolyethylene ether (T_(g)=168° C.) with in a ratio of 40 to 60%respectively, the resulting T_(g) would be 157° C. If the polymers areimmiscible or compatible, the blend will have two or more glasstransition temperatures characteristic of the individual polymers.

As described in prior art, both miscible and immiscible blends havedemonstrated an increase in mechanical properties compared to theproperties of each polymer in the blend assuming the appropriate mixingtechnique is used (Ibrahim & Kadum, 2010). With the use of amorphousPEEK in a polymer blend, extremely high-strength polymer blends for 3Dprinting result.

In another embodiment, the blended material may include two or morethermoplastic materials. In embodiments in which multiple materials areused to form the blended material, the total amount of each type ofmaterial should fall within the ratio guidelines provided above.

In yet another embodiment, a solid non-polymer filler material having ahigher melting temperature than the thermoplastic polymer material(s) isadded to the blend to improve mechanical properties of the printedobjects. The amount of the filler material by weight is up to about 60%,and more preferably between 5% and 20% of the total blend. The fillermaterial can include, without limitation, chopped carbon fibers, choppedglass fibers, chopped aramid/Kevlar fibers, continuous carbon fiber,continuous glass fiber, continuous polyethylene fiber, milled carbon,milled glass, graphite, graphene, carbon nanotubes, and graphenenanoplatelets. Preferably, the fibers are suspended and mixed in theblend during its fabrication. In an exemplary embodiment, the fibers aretreated or sized for the specific resin of choice and then encapsulatedor coated with resin to ensure sufficient wetting with the polymer.

Blending. If a blend of polymers (e.g., multiple amorphous polymers,amorphous and semi-crystalline polymers, etc.) is being prepared, it canbe prepared in accordance with method 100 depicted in FIG. 1. Thematerials to be blended are typically provided in pellet or powder form.

In step 101, the materials are dried in a dryer to remove moisture inorder to prevent hydrolysis of the polymer, which can reduce polymerchain length resulting in poorer properties. In step 102, the driedmaterials in powder form are physically and thoroughly mixed in a mixingdevice. In step 103, the mix is then fed to a hopper of an extruder. Insome embodiments, a single-screw or a twin-screw extruder is used tomelt blend the materials and then extrude the blended material into astrand.

In embodiments in which a filler material is used, it can be addedduring steps 102 or 103 or in step 201, discussed later herein. In theextruder, the mixed materials are “melted” (step 104). In accordancewith one embodiment, the melt blending is performed at a temperaturethat is:

-   -   (a) above the glass transition temperature of the amorphous        polymer materials, preferably at a temperature at which the        polymer is fluid;    -   (b) above the melting point of semi-crystalline polymer        materials (if present); and    -   (c) below the polymer degradation temperature of all amorphous        and semi-crystalline materials.

A typical melt blend temperature for the various PAEK polymers will bein the range of about 360 to about 370° C.

In embodiments in which more than one amorphous polymer material is usedin the blend, the melt blending is performed at a temperature that isabove the glass transition temperature of all the amorphous polymermaterials, at which the polymers behave like a fluid. Likewise, inembodiments in which more than one semi-crystalline polymer material isused, the melt blending is performed at a temperature that is above themelting point of all the semi-crystalline polymer materials that areused in the blend.

In step 105, the melted material passes through a die of an extruder(e.g., a single-screw extruder, a twin-screw extruder, etc.) and isextruded. In some embodiments, the resulting extrudate is formed into astrand, which is typically about 6 to 13 millimeters (¼-½ inch) indiameter. The melt processing temperature (i.e., the temperature of thematerial as it is extruded through an extrusion head) will typically benear the temperature at which the materials are melt blended.

Of course, the melt processing temperature for the blended material willbe dictated by the highest melting temperature or highest glasstransition temperature of all the amorphous and semi-crystallinematerials in the blend, whichever is higher.

After extrusion, in step 106, the strand is cooled, such as in a waterbath. In some embodiments, the size of the extrusion die is such thatthe strand is in a form of a filament having a diameter of 1-2 mm. Instep 107A, the filament is wound as a roll of filament, which can be feddirectly to a 3D printer (based on material extrusion or directed energydeposition processing).

Alternatively, in step 107B, the strand is cut into small pellets forstorage. In this case, the pellets are reprocessed into a filament of1-2 mm in diameter, which is adapted for direct feeding into a 3Dprinter (based on material extrusion or directed energy depositionprocessing) as illustrated in FIG. 2.

In step 201, the pellets containing the blended materials from step 107Bare fed into a hopper of an extruder, such as a single or twin-screwextruder. If the filler material is to be added, it can be added in thisstep instead of step 102 or 103. In step 202, the blended pellets are“melted” in the extruder. Similar to step 104, the melting is performedat a temperature that is:

-   -   (a) above the glass transition temperature of the amorphous        polymer materials, preferably at a temperature at which the        polymer is fluid;    -   (b) above the melting point of semi-crystalline polymer        materials (to the extent present); and    -   (c) below the polymer degradation temperature of all amorphous        and semi-crystalline materials.        The temperature in the extruder will typically be about 370 to        about 380° C.

In step 203, the melted material passes through a die of the extruderand is extruded into a filament, which is typically 1 to 2 mm indiameter. After extrusion, in step 204, the filament is cooled, such asin a water bath and is rolled onto a roll as a final product in step205, which is suitable to be fed directly into a 3D printer (based onmaterial extrusion or directed energy deposition processing).

To print a 3D object, the filament from the filament roll of theheat-blended material is fed to the 3D printer (based on materialextrusion or directed energy deposition processing). The filament isthen heated (e.g., by a heater block of the 3D printer to a temperaturethat is above the glass transition temperature of the amorphous materialand the melting point of the semi-crystalline material (if present).Typical printing temperature for amorphous PAEK and blends in accordancewith the present teachings will be in the range of about 350 to about370° C. The 3D printer then deposits the heated material in a selectedpattern layer-by-layer in accordance with a mathematical model of the 3Dobject in order to fabricate the object.

1-53. (canceled)
 54. A composition for use with a three-dimensional (3D)printer, comprising a first compound and a second compound differentthan the first compound, wherein the first compound is apolyaryletherketone (PAEK), and wherein the composition is amorphous.55. The composition of claim 54, wherein the second compound comprisesan additional PAEK.
 56. The composition of claim 55, wherein the PAEK ismore amorphous than the additional PAEK.
 57. The composition of claim54, wherein the second compound does not include a PAEK.
 58. Thecomposition of claim 54, wherein the PAEK is polyetherketone,polyetherketoneketone, polyetheretherketoneketone, orpolyetherketoneetherketoneketone.
 59. The composition of claim 58,wherein the PAEK is polyetherketone.
 60. The composition of claim 58,wherein the PAEK is polyetheretherketone.
 61. The composition of claim58, wherein the PAEK is polyetheretherketoneketone.
 62. The compositionof claim 54, further comprising a filler material having a meltingtemperature that is greater than a glass transition temperature of thePAEK.
 63. The composition of claim 62, wherein the filler materialcomprises one or more members selected from the group consisting ofchopped carbon fibers, chopped glass fibers, chopped aramid fibers,continuous carbon fiber, continuous glass fiber, continuous polyethylenefiber, milled carbon, milled glass, graphite, graphene, carbonnanotubes, and graphene nanoplatelets.
 64. The composition of claim 63,wherein the filler material comprises carbon nanotubes.
 65. Thecomposition of claim 63, wherein the filler material comprisescontinuous carbon fiber.
 66. The composition of claim 62, wherein thefiller material is encapsulated within the PAEK.
 67. The composition ofclaim 54, wherein a weight ratio of the first compound to the secondcompound is at least 1:1.
 68. The composition of claim 67, wherein theweight ratio is from about 1:1 to 19:1.
 69. The composition of claim 54,wherein the composition is included in a filament.
 70. The compositionof claim 69, wherein a diameter of the filament is from about 6millimeters (mm) to 13 mm.
 71. The composition of claim 69, wherein adiameter of the filament is from about 1 mm to 2 mm.
 72. The compositionof claim 54, wherein the composition is included in a pellet.
 73. Thecomposition of claim 54, wherein the composition is included in amaterial roll.